Physics group > Bounce group > Bouncing Particles on Layers

A cool feature of Trapcode Particular is being able to bounce particles on layers. Trapcode Particular supports bouncing particles on two 3D layers in the composition; the floor and wall. These two layers must be still in world space. By this, we mean that they cannot contain keyframes on rotation, scale or position properties. However, the camera can move freely in the scene as particles bounce on the layers.
Step-by-step instructions

Create a new comp (Ctrl/Cmd-N). Set the composition to be 640*480, with a frame rate of 30 and length of 5 seconds. Name it 'Main'. Create a new comp-sized Solid (Ctrl/Cmd-Y). Name it 'Particles', click the Make Comp Size button, and click OK. Apply Effect > Trapcode > Particular to the Solid.

Set the Particular Emission Controls

In Particular, set the following values:
Open the Emitter group and set Emitter > Position XY control to 320,100 (this will move the emitter upwards)
Open the Particle group and set the Particle > Life control to 5 (so particles live for 5 seconds) also set Particle > Color to Red
Open the Physics group and set the Physics > Gravity control to 300.
A RAM preview gives this:

A Ram preview of the initial particle set-up

Set-up the Floor

Now, let's add a floor so the particles have something to bounce on.
Create a 200*200 gray solid and name it "Floor".
In the Timeline, check the 3D switch on the Floor layer.
With the Floor layer selected, press the 'r' key to reveal the Rotation properties, and then set the Floor Rotation X to -90. Notice that the blue orientation arrow of the Floor now points upwards. This is important later when we want particles to bounce on the layer. If we had set 90 degrees (no minus) the blue arrow would have pointed downwards and particles would not bounce on the surface (they would go through the layer and then bounce).
Again with the Floor layer selected, press the 'p' key to reveal the Position property, and set the position value to 320,400,0

Add A Camera

To be able to navigate easily in the scene, create a composition camera.
Select Layer > New > Camera and select the 28mm preset, then press Ok. The Comp preview window will look the same but you can now reposition the view.

Set the Particular Physics Controls

To let Particular know that we want to bounce particles on the floor, the Physics group controls need to be set to the Bounce mode.
Select the Particles layer again and return to the Physics group of controls in the Particular plug-in.
Change the Physics > Physics Model menu to Bounce.
Open the Bounce subgroup, and set the Physics > Bounce > Floor Layer menu to Floor (the layer named Floor that you created earlier).

Set-up the Proper Visibility

You may notice a problem immediately, the Floor layer seems to be obscuring all the particles. To fix this:
Move the Floor layer below the Particle layer in the Timeline window.
OK, better, but now the particles are always in front of the floor. Here is the clever part, Trapcode Particular can use the floor to obscure particles that are behind it.
Open the Visibility group, and set the Visibility > Also Obscure With menu to All. This means all layers that Particular is linked to including Bounce layers will be used to obscure particles.
Now try orbiting around the scene and see how particles are correctly obscured by the floor.
OK, let's move on with the bouncing. Try a ram preview:

A Ram preview of the Particles bouncing off of the Floor layer.

The particles bounce but they do not recognize the size of the floor. To fix this problem, simply set the Physics > Bounce > Floor Mode menu option to Layer Size.

Adding a Second Bounce Layer

N ow let's add a text layer to the Comp and make particles bounce off the text as well as the floor.
Create a new composition, 400*100 with a frame rate of 30fps, and a duration of 5 seconds. Name the new Composition "Bounce".
Inside the Bounce Composition, use the Text tool and type "bounce" so it roughly fills the comp.

The new Bounce Comp with the Bounce Text

Go back to the Main comp and drag the Bounce comp into the comp window.
In the Timeline, check the 3D switch on the Bounce layer.
Select the Bounce layer in the Timeline, press the 'p' key to reveal the Position properties, and then set the layer's Position to 320,240,0
Press the 'r' key to reveal the Rotation properties for the Bounce Layer, and then set the Bounce Rotation X to -60. Set the Bounce layer's Rotation Y to 20.
Reorder the layers in the Timeline so that the Bounce layer is below the Particles layer in the Timeline window.

Add a Wall to the Particular Simulation

Select the Particles layer again and return to the Physics group of controls in the Particular plug-in.
Set the Physics > Bounce > Wall Layer menu to Bounce
Set the Physics > Bounce > Wall Mode menu to Layer Alpha (so particles bounce only where there is alpha)
Change the Emitter > Particles/sec control to 1000 to create more abundant particles (this will make it easier to see the two different bounce layers in action).

The Bounce and Floor layers reflecting particles created by Particular.

Experiment with the Other Collision Modes
Try setting Physics > Bounce > Collision Event menu to the Stick option and then RAM preview. This will cause the particles to stick to the Bounce and Floor layers as the Particles are emitted.
Try setting the Physics > Bounce > Collision Event menu to the Slide option to make particles slide off of the layers like they were made of ice.